Surface enhanced Raman spectroscopy (SERS) is a highly sensitive detection platform for chemical and biological agents due to the enhancement of the Raman scattering in close vicinity (<10 nm) of nanostructured metal surfaces. In most cases, this technique has been used to identify a single component analyte, or an analyte that has unique peak locations that are different from the background. For real applications, such as detecting particular chemical and biological agents from clinically relevant samples, the mixture could generate a complicated SERS spectrum. The abundance of spectral information in the spectrum makes extracting individual spectral components from that of a mixture a challenge for real-world applications of SERS. Multivariate analyses, e.g., principle component analysis (PCA), are commonly utilized to classify complex SERS spectra and/or distinguish individual components from mixtures. However, difficulties in establishing a complete library of all possible combinations of analytes of interest necessary for building statistical models, as well as in precluding interference from fluctuating environmental contaminants has posed major obstacles for this strategy. In order for SERS to be applied in more realistic situations, a simple means to physically separate the components of a mixture sample prior to SERS detection is necessary.
Thin-layer chromatography (TLC) is a well-established method used for separating components from mixtures. This method is simple and can be used to process multiple samples and standards simultaneously. In TLC the test sample is first spotted onto a thin layer of porous stationary phase (e.g., SiO2 gel) and allowed to dry. During plate development, the mobile phase (i.e., mixture of organic solvents) propagates along the TLC plate via capillary action, allowing the individual components to migrate along the solvent migration direction and spatially redistribute as a function of their varying affinity between the stationary and mobile phases. The separated components are identified by comparing the retention factors (Rf, the distance travelled by a component divided by the distance travelled by the solvent) with that of standards, or by coupling with gas chromatography (GC), infrared spectroscopy (IR), nuclear magnetic resonance (NMR), or mass spectrometry (MS), but the procedures involved are time-consuming and labor-intensive.